Truss Terminology S-Z


Covering on the ridge of the roof so that water will drain. Also called cricket.


Member fastened by nails to another member for reinforcement.

Scissors Truss

Dual pitch, triangular truss with dual pitched bottom chords.


Opening in a roof or parapet usually faced with metal flashing to drain water from the roof at a given point.

Sealed Drawings

Drawings prepared, checked and/or approved by and having the seal of a registered professional engineer or architect.

Self-Drilling Tapping Screw

A screw meeting the mechanical and performance requirements of SAE International Standard J78 that can drill a hole and form or cut mating threads in materials into which it is driven.

Set Back

Distance from the outside edge of the wall exclusive of veneer to the face of a girder truss.


Manufacturing term for a run of trusses of the same design currently being manufactured.


(1) Longitudinal separation of the wood. Generally two forms of shake are recognized, although variations and combinations may be used in industrial definitions. (2) Rectangular, board-like element for roof cover construction, similar to shingles.


Relative displacement of adjacent planes in a member.

Shear Stress

State of stress where internal adjacent planes in a member tend to slip on one another.

Short Member Installation Lateral Restraint

Short, structural members fastened at right angles to the Truss chords during installation of the Trusses for the purpose of reducing the laterally unsupported length of the Truss member.


Horizontal wood member forming the lowest part of the framework of a construction.


Two inch dimension lumber inserted between the top and bottom chords at the heel joint in the plane of the truss to reinforce the top or bottom chord.

Sloped Soffit

Sloped overhang with no level return.


Level return or underside of an overhang or truss cantilever end.

Soffit Vents

Prefabricated soffit material with perforated openings created for the purpose of providing intake ventilation.


Horizontal distance between outside edges of exterior bearings.

Specific Gravity

The ratio of the ovendry weight of a sample of wood to the weight of a volume of water equal to the volume of the wood sample at some specific moisture content, as green, air-dry, or ovendry.


Location at which two chord members are joined together to form a single member. It may occur at a panel point or between panel points.

Spreader Bar

A specifically designed lifting device that enables the lifting cables to hang straight or toe-in to their points of connection so as not to induce buckling forces in the Truss being lifted.

Square Cut

End of top chord perpendicular to the slope of the member. Cut made at 90ยบ to the length of the member.

Stacked Chords

In agricultural trusses when two members are positioned on top of each other to create a bottom chord.

Stacked Web Reinforcement

Reinforcement member attached to the Web at the Truss plant to avoid the need for field-installed reinforcement or Lateral Restraint and Bracing.

Step Down Truss

Truss used in a hip set roof system. Each step down truss has the same span and overhang as the adjacent standard trusses, but decreases in height with the top and bottom chords of its centered portion parallel to each other and horizontal. See also Hip Set.

Stick Framing

See conventional framing.


The Spreader Bar when it is brought down alongside, and attached directly to the Truss being lifted to provide sufficient rigidity to adequately resist out-of-plane bending of the Truss. See Spreader Bar.


Force per unit of area.

Stress-Graded Lumber

Lumber of any thickness and width that is graded for its mechanical properties.

Strongback Bridging

Two-inch dimensional framing member attached perpendicular to floor trusses - often through the chase opening - and placed vertically against the vertical web.

Structural Board

Board graded for structural applications requiring stress grading for assignment of allowable properties. Also referred to as a Stress Rated Board.

Structural Building Components

Specialized structural building products designed, engineered and manufactured under controlled conditions for a specific application. They are incorporated into the overall building structural system by the Building Designer. Examples are wood or steel roof trusses, floor trusses, floor panels, wall panels, I-joists, or engineered beams and headers.

Structural Element

A single joist, rafter, beam, or other structural member (not including the Trusses) designed by others and supplied for the Building Structural System by either the Truss Manufacturer or others.

Structural Element Submittals

Documentation relating to the Structural Elements that are supplied by the Truss Manufacturer, if required by the Contract, submitted by the Truss Manufacturer to the Local Building Official, Owner, Building Designer and/or Contractor for their review and/or approval.

Structural Sheathing

The structural covering used directly over the roof, floor or wall framing members that transfers perpendicular Loads to the framing members. Structural Sheathing commonly used with Trusses includes plywood, oriented strand board (OSB), and certain types of metal decking. Properly sized and installed Structural Sheathing provides both Lateral Restraint and stability to the Truss members.

Stub Truss

Truss that is shortened in length but maintains the original profile.


One of a series of slender wood structural members used as supporting elements in walls and partitions. In softwood grading, a stress grade to describe lumber suitable for stud use.

Studded Gable

Gable end frame built as a wall and resembling a stud wall built in the shape of a triangle. Chords are usually on the flat.

Submittal Documents

Construction Documents, special inspection and structural observation programs, data, guides, reports, and manufacturer's installation instructions submitted for approval with each permit application or available at the jobsite at the time of inspection.


Surface upon which the roofing membrane is placed.


A piece of lumber attached to a web as reinforcement against buckling instability. The T-brace is installed so that in cross-section it forms a letter "T" with the web. See also Web Reinforcement.

Temporary Bracing

Bracing installed for the purpose of holding trusses true to line, dimension and plumb. In addition, temporary bracing holds trusses in a stable condition until permanent truss bracing and other permanent components that contribute to the overall rigidity of the roof or floor are in place. Temporary bracing may consist of ground bracing, continuous lateral sheets or ties, diagonals, cross-bracing or similar items. See WTCA Job Site Warning Poster and the Always Diagonally Brace for Safety TTB for more information.

Tension Parallel-To-Grain

Imposition of a tensile stress that acts in a direction parallel to the fiber direction of the wood.

Tension Perpendicular-To-Grain

Imposition of a tensile stress that sets in a direction perpendicular to the fiber direction of the wood.


Outward horizontal force.


Nail driven at an angle to the member.

Top Chord

Inclined or horizontal member that establishes the top member of a truss.

Top Chord Bearing

Bearing condition of a parallel chord truss that bears on its top chord extension. Can also apply to a sloping chord truss bearing on a top chord extension.

Top Chord Installation Lateral Restraint (TCILR)

Structural members installed at right angles to the Top Chord of a Truss during construction to reduce the laterally unsupported length of the Top Chord.

Seismic Load

Assumed lateral load acting in any horizontal direction on the structural frame due to the dynamic action of earthquakes.

Worker Lift

A machine intended to mechanically hoist a worker.


Tissues of the stem, branches, and roots of a woody plant lying between the pith and cambium, serving for water conduction, mechanical strength, and food storage, and characterized by the presence of tracheids or vessels.

Wind Speed

The design Wind Speed for the structure. The value is determined by the Building Designer, with the minimum determined by the building code in effect in the Jurisdiction where the structure is built.

Wind Load

Lateral pressure on the building or structure in pounds per square foot (psf), or the metric pascals (Pa), due to wind blowing in any direction.


Triangular piece of lumber that has one side equal to the standard 2" dimension lumber widths, and is inserted between the top and bottom chords, usually to allow the truss to cantilever. Its use is determined through engineering analysis.


Members that join the Top and Bottom Chords to form the triangular patterns typical of Trusses. These members typically carry axial forces.

Web Reinforcement

A piece of stress-rated lumber attached to a web as reinforcement against buckling instability. Types of web reinforcement include T-bracing, L-bracing, scab bracing and metal reinforcement. The length of the reinforcement is up to 90% the length of the web.

Web Member

Members that join the top and bottom chords to form the triangular patterns typical of trusses. These members typically carry axial forces.


Any variation from a true or plan surface. Warp includes bow, crook, cup, and twist, or any combination thereof.


Bark or lack of wood from any cause on edge or corner of a piece.

Web Member Plane

The two-dimensional area formed by the top or bottom edge of adjacent similar web members allowing for the connection of Lateral Restraint and Bracing members.

Visual Grade Lumber

Type of lumber that has been visually rated at the lumber mill for structural properties through rules established by the national lumber associations.

Valley Truss

Not a truss, but traditionally called so. Set of triangular components used to frame the shape of dormers and to complete the roof framing where trusses intersect at perpendicular corners. Valley members usually require support at a maximum distance of 24".

Valley Set

Set of triangular components used to frame the shape of dormers and to complete the roof framing where Trusses intersect at perpendicular corners.


Depression in a roof where two roof slopes meet.

Uniform Load

Total load that is equally distributed over a given length, usually expressed in pounds per lineal foot (plf)

Truss System Engineer

A Licensed Engineer who designs a Truss System.

Truss System

An assemblage of Trusses and Girder Trusses, together with all Bracing, Connections, and other Structural Elements and all spacing and location criteria, that, in combination, function to support the dead, live and Wind Loads applicable to the roof of a structure with respect to a Truss System for the roof, and the floor of a structure with respect to a Truss System for the floor. A Truss System does not include walls, foundations or any other structural support systems.

Truss Submittals

The Truss Design Drawings, and the Truss Placement Plan if required by the Contract, submitted to the Local Building Official, Owner, Building Designer and/or Contractor for their review and/or approval.

Truss Submittal Package

Package consisting of each individual Truss Design Drawing, and, as applicable, the Truss Placement Diagram, the Cover/Truss Index Sheet, Lateral Restraint and Diagonal Bracing details designed in accordance with generally accepted engineering practice, applicable BCSI defined Lateral Restraint and Diagonal Bracing details, and any other structural details germane to the trusses.


Distortion caused by the turning or winding of the edges of a board so that the four corners or any face are no longer in the same plane.

Truss Span

The horizontal distance between outside edges of exterior bearings.

Truss Spacing

On-center distance between trusses.

Truss Profile

A side view representation or outline of a Truss.

Truss Placement Diagram (TPD)

Illustration identifying the assumed location of each Truss.

Truss Orientation

The Truss position or alignment within a structure relative to bearing walls.

Truss Manufacturer

An individual or organization regularly engaged in the manufacturing of Trusses and who manufactures Trusses and who may supply Structural Elements for the Building Structural System.

Truss Heel Height

The vertical depth of the Truss at the outside face of bearing.

Truss Designer

Person responsible for the preparation of the Truss Design Drawings. The individual or organization responsible for the design of Trusses in accordance with this Standard, the Truss Design Standard and all Legal Requirements. The Truss Designer is also referred to as a Truss Design Engineer when the Truss design calculations and/or Truss Design Drawings resulting from the design of the Trusses shall be sealed by an Engineer.

Truss Design Standard

The latest approved edition of ANSI/TPI 1 National Design Standard for Metal Plate Connected Wood Truss Construction.

Truss Design Engineer

Person who is licensed to practice engineering as defined by the Legal Requirements of the Jurisdiction in which the Building is to be constructed and who supervises the preparation of the Truss Design Drawings.

Truss Design Drawing

Written, graphic and pictorial depiction of an individual Truss.


Individual metal plate connected wood component manufactured for the construction of a Building.


Conventionally framed wall usually consisting of fastened multiple studs in a framed wall opening, used to carry the header reactions.


The act of forming rigid triangles with objects adequately fastened together.


Directions in wood at right angles to the wood fibers. Includes radial and tangential directions. A transverse section is a section through a tree or timber at right angles to the pitch.

Top Plate

Framing consisting of two members on the flat that form the top of exterior stud bearing walls of platform frame construction. A single member on the flat in non-bearing wall construction.

Top Chord Plane

The two-dimensional area formed by the top or bottom edge of adjacent similar Top Chords allowing for the connection of a roof Diaphragm, or Bracing members in a linear fashion.